1. Field of Invention
The invention relates to an internal combustion engine for a vehicle, and more particularly, to a technology for controlling start of the internal combustion engine.
2. Description of Related Art
Recently, an electric motor has been generally used for driving (cranking) a crankshaft upon start of the internal combustion engine. The aforementioned electric motor is required to drive the crankshaft against the force generated by compression gas within the cylinder and frictions among the respective elements of the internal combustion engine. As a result, the rating and power consumption of the electric motor is likely to be increased.
Especially the system for automatically stopping the operation of the internal combustion engine upon stop of the vehicle, that is, idling stop system, is required to re-start the internal combustion engine immediately in response to the request of the vehicle operator to re-start. The resultant load exerted to the electric motor is increased, which may lead to increase in both rating and power consumption of the electric motor.
There is a technology proposed for reducing the load exerted to the electric motor by operating the electric motor to rotate the crankshaft in the reverse direction temporarily before cranking starts such that the resultant gas compression force is used for the cranking (see Related Art No. 1, i.e., JP-A-6-64451).
Related Art 2, i.e., JP-A-2002-147319 discloses the technology in which the crankshaft is rotated in the reverse direction when its rotation in the normal direction stops until the moment just before the intake valve of the cylinder positioned just before the top dead center in the compression stroke is opened. This may cause the piston ring to be floated within the piston ring groove such that the pressure within the cylinder is released. The resistance caused by the compression pressure within the cylinder is reduced when the crankshaft is rotated in the normal direction for performing the cranking easily. Alternatively, the piston in a stopped state is set to a position immediately after the top dead center in the compression stroke so as to improve starting ability of the internal combustion engine (see Related Art 3, i.e., JP-A-2002-130095).
In another technology, the fuel is directly injected into a combustion chamber of the cylinder in intake stroke or compression stroke upon start of the internal combustion engine so as to reduce the driving torque required for starting the engine by the combustion torque generated by combusting the fuel, resulting in improved starting ability (see Related Art 4, that is, JP-A-11-159374), for example. The list of Related Art will be described below:
JP-A-6-64451;
JP-A-2002-147319;
JP-A-2002-130095; and
JP-A-11-159874.
In the aforementioned technology as related art, the gas compressive force is likely to be reduced in case of small quantity of residual gas within the cylinder of the internal combustion engine or the low temperature within the cylinder. This may prevent sufficient reduction in the load exerted to the electric motor.